Abstract: This paper presents a solution to the LFC problem based on PSO and genetic algorithm (GA). The controller is constructed for a two-area interconnected thermal-hydro power system. The dynamic model of the power system and the controller design based on the model are elaborated in this paper. Exhaustive simulations are carried out using MATLAB/Simulink platform in order to verify the performance of PID controller in LFC problem under various dynamic conditions. Simulation results proved that PSO tuned controller is attractive to the LFC problem in its stability and robustness.